Question

The sum of three numbers is 6. When second number is subtracted from thrice the sum of first and third number, we get number 10. Four times the sum of third number is subtracted from five times the sum of first and second number, the result is 3. Using above information, find these three numbers by matrix method.

Answer 1

Given that the sum of three numbers, x, y and z is 6.
From the given statement, we have,
x + y + z = 6
3 ( x + z ) -  y = 10 
5 ( x + y ) -  4z = 3
Thus, the system of equations are :
x + y + z = 6                                 (i)
3x - y + 3z = 10                            (ii)
5x + 5y - 4z = 3                            (iii)
Let us write the above equations in the matrix form as:

`[[1,1,1],[3,-1,3],[5,5,-4]][[x],[y],[z]]=[[6],[10],[3]]`

AX = B

`"A" = [[1,1,1],[3,-1,3],[5,5,-4]], "X" = [[x],[y],[z]],  "B" = [[6],[10],[3]]`

Applying R_3→ R₃- 5R₁ , we have

`[[1,1,1],[3,-1,3],[0,0,-9]][[x],[y],[z]]=[[6],[10],[-27]]`

 Applying R_{2 →} R₂ - 3R₁ , we get
`[[1,1,1],[0,-4,0],[0,0,-9]][[x],[y],[z]]=[[6],[-8],[-27]]`

Thus,
x + y + z = 6                                   [From(i)]
- 4y = - 8                                                 (iv)
- 9z = - 27                                                (v)
From equation (iv), we get
y = 2
From equation (v), we get
z = 3
Putting the value of y and z in equation (i), we get x = 6 - 2 - 3 = 1
Hence, numbers are 1, 2, and 3.